<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
*{margin: 0;padding: 0;border: 0;}
input{width:300px;height:50px;line-height:50px;float: left;border:red 1px solid;}
.bottom_f{width:100%;height:50px;background-color: red;position: fixed;left:0;bottom:0;}
</style>
</head>
<body>
	<input id="kai" placeholder="kailong">
	<div class="bottom_f" id="b_t"></div>
	<script>
		kai.addEventListener('focus', function (e) {
			console.dir(b_t.style.position = 'static');
			return true;
		});
		kai.addEventListener('blur', function (e) {
			console.dir(b_t.style.position = 'fixed');
			return true;
		});
	</script>
</body>
</html>